The present disclosure relates to an apparatus for measuring a multi-fluid flow having entrained gas therein, and more particularly to an apparatus that measures the speed of sound propagating through the multi-fluid flow to determine the gas volume fraction of the gas in the process flow and compensating the output measurement of a fluid cut measurement device for entrained gas.
A fluid flow process (flow process) includes any process that involves the flow of fluid through pipe, ducts, or other conduits, as well as through fluid control devices such as pumps, valves, orifices, heat exchangers, and the like. Flow processes are found in many different industries such as the oil and gas industry, refining, food and beverage industry, chemical and petrochemical industry, pulp and paper industry, power generation, pharmaceutical industry, and water and wastewater treatment industry. The fluid within the flow process may be a single phase fluid (e.g., gas, liquid or liquid/liquid mixture) and/or a multi-phase mixture (e.g. paper and pulp slurries or other solid/liquid mixtures). The multi-phase mixture may be a two-phase liquid/gas mixture, a solid/gas mixture or a solid/liquid mixture, gas entrained liquid or a three-phase mixture.
In certain flow processes, such as those found in the oil and gas industries, it is desirable to separate liquid (e.g., oil and/or water) and gas (e.g., air) components of a fluid. This is typically accomplished using a separator, which is an item of production equipment used to separate liquid components of the fluid stream from gaseous components. The liquid and gas components flow from the separator in separate legs (pipes), with the leg containing the gas component referred to as the “gas leg” and the leg containing the liquid component(s) referred to as the “liquid leg”.
Driven by goals of reducing size and cost of conventional three phase separation approaches, many operators have adopted approaches that utilize smaller, two-phase, gas/liquid separation in conjunction with flow and water cut measurement to measure net oil. Many techniques are used for gas/liquid separation, including level-controlled batch tank separators and continuous flow cyclonic separators.
Typically, there are three methods widely used to determine water cut and, in turn, net oil: 1) density measurement via a Coriolis meter. 2) frequency of a resonant microwave oscillator, and 3) absorption of microwave energy. Problematically, the presence of free gas in any of these devices can result in significant over-reporting of net oil.
Although most gas/liquid separator-based net oil measurement approaches are designed to eliminate gases in the liquid leg of the separator, it has proved difficult to ensure complete gas/liquid separation. Furthermore, since the fluid exits the separator at, or near, vapor pressure, additional outgassing from the liquid can occur prior to measurement due to pressure losses in the flowing mixture. As a result, errors in oil fraction measurement attributed to the entrained gasses can often be the single largest source of error in net oil measurement.
Thus, there remains a need for an apparatus to compensate for entrained gas within a multi-liquid mixture to provide an accurate fluid cut of the liquids in the mixture.